Numbers can come to ballplayers in the most mundane, random ways. More often than not, as in the case of Mariano Rivera, a jersey is literally tossed to the player by an equipment man giving little or no thought to any particular meaning the number on the back might one day carry.
It is up to the athlete to make the number his own, to give it an identity in its attachment to his achievements. It can become a permanent accessory to his legacy, or it can be discarded and handed over to another young dreamer after the player moves on to another team or into obscurity.
If a player goes on to leave a huge imprint on his franchise and the sport and has his number retired, it will not be worn again by anyone else on that team.
Retiring a number is a process taken very seriously by all Major League organizations. Different philosophies come into play. Some clubs choose only to retire a number after the player has been elected to the Hall of Fame. Others are more liberal, granting the distinction to players or contributors for extraordinary service or special circumstances.
In 1997, in recognition of his unprecedented social impact on the game, Jackie Robinson's No. 42 was retired in all MLB ballparks. It would be worn for the last time by Rivera, the king of closers who retired following the 2013 season.
No organization retires jersey numbers with the majesty of Rivera's New York Yankees, whose history and tradition stand alone. They have done it 16 times for 17 legends, more than any other team, and they upped the ante in terms of festivities with their celebration of Rivera last Sept. 22 with six games left in their season.
Personally and carefully unveiling his pinstriped No. 42 in Monument Park that sun-splashed day, Rivera acknowledged with arms outstretched a roaring ovation from the 49,197 fans who rose and chanted his name.
In characteristically dignified manner, Rivera paid tribute to the original 42, Robinson, whose wife, Rachel, and daughter, Sharon, were on hand for the ceremony.
"To have Rachel and the Robinson family here, it means a lot to me," Rivera said. "All the respect that I have for the family and for Mr. Jackie Robinson and all he did for us, me being the last one to wear the No. 42, I can't ask for better than that."
Giving it the civic seal of approval, mayor Michael R. Bloomberg proclaimed "Mariano Rivera Day" in the City of New York, and a wave of Panamanian flags in Yankee Stadium demonstrated his native land's pride in the Sandman.
Jerry Coleman, the late, great Yankees second baseman and war hero, wore 42 in pinstripes from 1949-57.
Celebrations similar to Rivera's will play out in the Bronx when Derek Jeter's No. 2 and new Hall of Famer Joe Torre's No. 6 are retired. Jeter is a slam dunk, and Yankees general manager Brian Cashman has made it clear Torre's 6 is destined for Monument Park. This will leave no single-digit numbers available to Yankees players. No. 8, worn by Bill Dickey and Yogi Berra, was retired twice. The lowest number available will be 11, with Phil Rizzuto's 10 retired.
"We haven't given  out for a reason," Cashman said this spring. "It's been tucked away for quite some time. At some point, that will happen, no doubt about it. Clearly, it's already unofficially happened because we've left that open."
The Yankees also have not handed over Bernie Williams' 51 or Jorge Posada's 20 to another player. When Paul O'Neill's 21 went to reliever LaTroy Hawkins in 2008, negative fan reaction caused Hawkins to switch to 22.
After the Yankees, not including 42, St. Louis is next with 14 retired jerseys -- 12 by Cardinals players. No. 85 is for club owner August A. Busch, and broadcaster Jack Buck also is honored.
San Francisco's Giants and Cincinnati's Reds have 13 honorees. The Reds recognize three broadcasters (Joe Nuxhall, Waite Hoyt and Marty Brennaman), the Giants two (Russ Hodges and Lon Simmons).
Atlanta and the Los Angeles Dodgers have 10 retired jerseys, including Robinson for the Dodgers. Jim Gilliam (19) is the only non-Hall of Famer whose number is visible at Dodger Stadium. Interestingly, Steve Garvey's 6 was retired by the Padres, but not by the Dodgers. There are those in L.A. clamoring for the club to retire Maury Wills' No. 30 and Fernando Valenzuela's 34, but neither meets the club's Hall of Fame criterion.
Pittsburgh, Houston and the White Sox have nine retired numbers, Detroit and Philadelphia eight. Boston, the Cubs, Cleveland, San Diego and Minnesota have seven. Baltimore and Oakland have six retired numbers, the Angels and Montreal/Washington five. Milwaukee has four, Kansas City and the Mets three. Texas (Nolan Ryan and Johnny Oates) has two, Tampa Bay (Wade Boggs), Toronto (Roberto Alomar), Arizona (Luis Gonzalez) and Miami (Carl Barger) one each.
Colorado will retire first baseman Todd Helton's No. 17 on Aug. 17, making him the first Rockies player so honored. Seattle has yet to retire a number of one of its own, but it's only a matter of time.
Robinson Cano wore No. 24 -- 42 reversed -- most of his Yankees career. Arriving in Seattle, Cano chose 22 in deference to the great Ken Griffey Jr. The club policy is that a six-year hold is on a player after he's left the game, waiting until he's appeared on one ballot for the National Baseball Hall of Fame. Randy Johnson and Ichiro Suzuki have both made 51 famous in Seattle.
"No, I would never talk to [Griffey] about 24," Cano said in response to a question about his choice of No. 22. "He's a guy you have to show respect. If that was going to happen, it would have to come from him. We all know what he meant to this city and who he was and what kind of player. He's a future Hall of Famer. You don't go to a Hall of Famer and ask, 'Can I use your number?' You have to show him respect."
Nolan Ryan has had his number retired three times: 34 by the Rangers and Astros, and 30 by the Angels. Hank Aaron's No. 44 is retired by the Braves and Milwaukee Brewers. Frank Robinson's 20 will never be worn again by the Reds and Orioles.
Rod Carew's 19 is retired by the Twins and Angels. Reggie Jackson's No. 9 is visible in Oakland, and his 44 is in the Yankees' Monument Park. Carlton Fisk's 27 is honored in Boston and his 72 by the White Sox. Rollie Fingers' 34 is retired by the A's and Brewers. The Cubs and Braves have each retired newly minted Hall of Famer Greg Maddux's 31.
Rivera was handed 42 by an equipment man in the spring of 1995. His initial reaction was delight; it meant he'd made the club coming off surgery. He soon came to understand the full significance of the number.
Never one to make waves, Rivera has given voice to his belief that the No. 21 worn by Hall of Famer Roberto Clemente ought to be retired all across MLB alongside Robinson's No. 42. Arriving in Pittsburgh in 1955, Clemente paved the road for a multitude of Latino players with his legendary play for the Pirates before dying at 38 years old in a plane crash off the coast of his native Puerto Rico.
Clemente was attempting to fly relief goods to earthquake victims in Nicaragua on Dec. 31, 1972. In a special election, he became the first Latin player elected to the Hall of Fame in 1973.
"One day it might happen [for Clemente's 21] -- we need to continue pushing toward that," Rivera said on April 15, 2013, when all MLB field personnel, in an annual rite, wore No. 42. "I'd like to see that happen. I mean, he was a great player. And he died helping people. Imagine. Just imagine."
Lyle Spencer is a columnist for MLB.com.